The present invention relates a sheet feeding mechanism, and more particularly to a sheet feeding mechanism for reliably feeding sheets such as sheet films, one by one, from a stack of stored sheets.
Radiation image recording apparatuses are in general use for recording radiation images on photosensitive films through exposure to X-rays for subsequent use in medical diagnosis or the like. The photographic films are loaded in the radiation image recording apparatus under light-shielded conditions so that the films will not be exposed to extraneous light. The image of an object is recorded on a loaded photographic film by exposing the emulsion layer of the film directly to X-rays.
There has recently been developed and widely used, particularly in the medical field, a radiation image recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays. When a stimulable phosphor is exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation.
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is recorded on a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image signal which is electrically processed to generate image information which is recorded on a recording medium such as a photographic photosensitive material or displayed as a visible image on a CRT or the like.
The visible image thus produced may be recorded on a recording medium by an image recorder such as an image output laser printer, for example. In the image output laser printer, photographic recording sheet films are stacked in a magazine, loaded, and taken out one by one by a sheet feeding mechanism including a suction cup or the like. Thereafter, the film is exposed to a laser beam modulated by an signal produced from the stimulable phosphor sheet for recording an image on the film. The exposed film is then transferred into an automatic developing device and processed thereby to develop the image. The film is thereafter stored in a prescribed place or directly used in medical diagnosis.
Films to be delivered by the sheet feeding mechanism are stacked in the magazine, and hence tend to stick to adjacent sheets due for example to static electricity. Therefore, when taking a film out of the magazine using the suction cup, one or more adjacent films are liable to stick to the film and hence a plurality of films are simultaneously fed from the magazine.
Japanese Laid-Open Paten Publication No. 56-132236 discloses a sheet feeding mechanism for taking films, one by one, out of magazine.
FIG. 1 of the accompanying drawings shows the disclosed sheet feeding mechanism, generally designated by the reference numeral 2. The sheet feeding mechanism 2 includes a support member 4 through which five tubular bodies 6a through 6e extend for slidable movement. Suction cups 8a through 8e are mounted on the distal ends of the tubular bodies 6a through 6e, respectively, and stoppers 10a through 10e are fixed to the tubular bodies 6a through 6e, respectively, at positions spaced given distances from the suction cups 8a through 8e. The stoppers 10a through 10e are located on the respective tubular bodies 6a through 6e such that when the support member 4 is positioned parallel to a sheet stack A, the suction cups 8a, 8e are closest to the sheet stack A, the suction cup 8c is remote from the sheet stack A, and the suction cups 8b, 8d are positioned between the suction cups 8a, 8e and the suction cup 8c. Coil springs 12a through 12e are disposed under compression between the suction cups 8a through 8e and the support member 4. The tubular bodies 6a through 6e are connected to a vacuum suction mechanism (not shown).
In operation, the support member 4 is displaced toward the sheet stack A until it reaches a position in which all of the suction cups 8a through 8e abut against the upper surface of an uppermost sheet A1. Then, the support member 4 is stopped, and the vacuum suction mechanism is actuated to cause the suction cups 8a through 8e to attract the sheet A1.
Then, the support member 4 is moved away from the sheet stack A. Upon such movement of the support member 4, the stopper 10c fixed to the tubular body 6c is first brought into engagement with the support member 4 under the influence of the coil spring 12c, thus displacing the suction cup 8c upwardly in FIG. 1. Therefore, a slight gap is created between the uppermost sheet A1 and next adjacent sheet A2. As the support member 4 is further displaced upwardly, the stoppers 10b, 10d are then brought into engagement with the support member 4 by the bias forces of the coil springs 12b, 12d to move the suction cups 8b, 8d upwardly. Finally, the suction cups 8a, 8e are moved upwardly, and hence all of the suction cups 8a through 8e are displaced upwardly to deform the sheet A1 in an upwardly curved shape as shown in FIG. 1.
Consequently, a space is developed between the sheets A1, A2, so that the sheet A2 will not be fed with the sheet A1. As a result, sheets can be fed one by one from the sheet stack A by the sheet feeding mechanism 2.
With the conventional sheet feeding mechanism 2, however, since the sheets are curved by the suction cups 8a through 8e, the lengths of the tubular bodies 6a through 6e on which the suction cups 8a through 8e are mounted, respectively, must be appropriately selected. More specifically, the tubular body 6c, the tubular bodies 6b, 6d, and the tubular bodies 6a, 6e have at least three respectively different lengths. This is disadvantageous in that the process of fabricating the tubular bodies is made more complex and costly. In addition, the tubular bodies must be associated with coil springs of different lengths, and it is also tedious and time-consuming to select suitable spring lengths, manufacture coil springs of such different lengths, and adjust the coil springs so as to best suited to the associated tubular bodies. Another drawback is that after the sheet A1 has been fed from the sheet stack A, the sheet A1 is held in the curved configuration, and, therefore, the feed path following the sheet feeding mechanism 2 should be of such a structure as to be able to accommodate the curved sheet A1. The feed path of such a structure is, however, complicated.